With configurations such as transmit diversity, MIMO (Multiple Input & Multiple Output), and a smart antenna, a wireless cellular base station requires timing alignment of transmission signals of multiple antennas. For example, as required by WCDMA (Wideband Code Division Multiple Access) protocols 3GPP TS 25.104 and TS 25.141, a signal delay difference between two transmitting antenna ports of a transmitting diversity or MIMO base station does not exceed +/−0.25 Tc (1 Tc is approximately 260 ns). LTE (Long Term Evolution) also imposes a similar requirement.
In practical application, various kinds of FIFO (First Input First Output) apparatuses (such as FIFO in an analog-to-digital converter and FIFO in a digital intermediate-frequency channel chip) on digital channels of a transmitter lead to a difference of a delay every time when a system is powered on. Meanwhile, a group delay of a transmitter analog channel also changes with a frequency, a temperature, and a batch of components. These factors all lead to drift of timing of a transmission signal at each antenna, and a system requirement can hardly be satisfied. Especially, when a multi-antenna system is assembled with multiple different batches of independent modules, such a problem is more obvious.
In a process of implementing the present invention, the inventor of the present invention finds that: In the prior art, it is difficult to observe and measure signals of two transmitters at antennas simultaneously, and it is generally incapable of using a closed-loop mechanism to detect and rectify signal alignment at a transmitting antenna. Therefore, in the prior art, top-down design is used to make delays between different channels consistent with each other. A general technical measure is to reduce FIFO steps on a digital channel as much as possible in design. For a delay change of an analog channel, a large amount of test data is used to generate a data table for compensation. This open-loop solution is difficult to implement, and is hardly accurate.